The present invention relates to a medical scalpel for incising spherical biological tissues, and in particular to a medical scalpel capable of producing a highly auto-closable incisional vulnus in eyeball incision.
In the conventional ophthalmic surgery, incision of cornea or interstice of cornea and sclera inevitably requires successive suture or ligation of incised cornea or sclera. A suture may, however, pressurize the cornea or sclera, which tends to retard recovery of eyesight or to produce postoperative astigmatism. So that recent trends in the surgery relate to production of auto-closable incisional vulnus which automatically closes without needing suture.
A preferable and highly auto-closable incisional vulnus will be explained referring to FIGS. 5A and 5B, and FIGS. 6A to 6C. As shown in FIG. 5A, when a cornea 52 is incised with a scalpel 51 in a direction oblique to the thickness thereof to produce an incisional vulnus 53 (this is generally done, in a front view of an eyeball, by piercing the scalpel 51 in a direction from lower to obliquely upper), intraocular pressure will be exerted to pressure-open the cornea 52 (in a direction energizing the cornea 52 along an arrow xe2x80x9caxe2x80x9d), to thereby close the incisional vulnus 53 by pressure contact.
While a morphology of such preferable, highly auto-closable incisional vulnus will differ whether it is viewed from a direction of the scalpel insertion or front of the eyeball since the eyeball has a spherical surface, a front view of the eyeball shows an external incisional line 53a formed on the external of the cornea 52, which is given as a straight line as shown in FIG. 6A, or as curved lines bulging toward an internal incisional line 53b as shown in FIGS. 6B and 6C.
The scalpel 51 used for incising the eyeball will now be described referring to the drawings. The scalpel 51 shown in FIG. 7A has a sharp pointed end 51a and peripheral cutting edges 51b, and that shown in FIG. 7B has a cutting edge 51b rounded along the entire periphery rather than having a pointed end. Sectional forms of such scalpel 51 being generally employed include a trapezoid having a virtual line connecting the cutting edge 51b as a base as shown in FIG. 7C (bevel-up type), and flattened hexagon having a line connecting the cutting edge 51b approximately at the center of the total thickness of the blade portion as shown in FIG. 7D (bi-bevel type).
In eyeball incision, the scalpel 51 is opposed to the cornea 52 so as to allow formation of the auto-closable incisional vulnus 53, and is forwarded straight along a direction indicated by arrow xe2x80x9cbxe2x80x9d in FIG. 5A. The scalpel 51 is then moved rightward or leftward according to a purpose of the surgery, to widen the incisional vulnus 53.
It is known that such preferable, highly auto-closable incisional vulnus has the external incisional line which gently curves as bulging toward the center of the eyeball or runs straight when viewed from the front of the eyeball. On the contrary, a less auto-closable incisional vulnus is known to have the external incisional line which gently curves as bulging away from the center of the eyeball when viewed from the front of the eyeball, and is likely to turn over when pressure is exerted on the cornea to thereby undesirably incorporate foreign matters or bacteria contained in lacrimal fluid into the eye, so that such vulnus needs suture to enhance auto-closable property. It has, however, been difficult to produce a preferable, highly auto-closable incision vulnus using a generally known scalpel.
More specifically, a bevel-up scalpel 51 shown in FIG. 8 causes on both planes of the blade portion thereof different amounts of force due to pressure p ascribable to the ocular tension and incision resistance when pierced into the cornea 52 (that is, downward force Fd exerted on the upper plane comprising an upper plane and a slant plane is larger than upward force Fu exerted on the base plane), so that the entire portion of the scalpel 51 will shift toward the base plane as it advances deeper into the eye. So that an incisional vulnus thus produced will have a reversed V-form when viewed from the direction of the scalpel insertion, which comprises a tip portion corresponding to the pointed end 51a and straight portions extending from such tip portion toward the ends. Such incisional vulnus will, however, have the tip portion and curves extending from the such tip portion when viewed from the front of the eyeball. Such tip portion is likely to dislocate and may cause astigmatism after the auto-closure.
The bi-bevel scalpel causes on both sides of the blade portion thereof balanced forces ascribable to the ocular tension and incision resistance, so that no vertical force enough for dislocating the scalpel will be generated The incisional vulnus thus produced will have a straight profile as viewed from the direction of the scalpel insertion, but will have an external incisional line bulging away from the center of the eyeball, which makes the incisional vulnus less auto-closable.
It is therefore an object of the present invention to provide a medical scalpel capable of producing a preferable, auto-closable incisional vulnus.
A medical scalpel of the present invention is such that for incising a spherical biological tissue which comprises a shank, and a planar blade portion being associated to said shank and having a first face and a second face one of which is formed flat at least wherein said blade portion having an edge in parallel as a whole with said flat first face or said second face, and being formed so as to have a ratio of the partial thickness thereof on one side of a virtual flat plane surrounded by said edge to the total thickness thereof which resides within a range from 75 to 93%.
Such medical scalpel (simply referred to as scalpel, hereinafter) has along the outer periphery of the blade portion at least two slopes composing both sides thereof, and the partial thickness of such blade portion on one side (the upper side, for example) of a virtual flat plane surrounded by such edge accounts for 75 to 93% of the total thickness of the blade portion. Such setting allows the force exerted on the upper side of the edge, that is the force pushing the scalpel downward, to become larger than the upward force exerted on the lower side.
Difference between the downward force and upward force is, however, smaller than that in the conventional bevel-up scalpel by virtue of cancellation therebetween, so that a slight downward dislocation of the scalpel will occur when the scalpel is pierced into the eyeball, to thereby produce the external incisional line gently bulging toward the center of the eyeball or extending straightly when viewed from the front of the eyeball. Hence, the external incisional line can have a profile equivalent to that illustrated in FIG. 6C, to thereby produce a preferable, highly auto-closable incisional vulnus.
The force exerted on the blade portion along the direction from the upper face side to the lower face side when the edge is pierced into the eyeball can properly be adjusted by selecting the upper partial thickness within a range from 75 to 93% of the total thickness, which defines the travel distance of such blade portion from the upper face side to the lower face side. Thus the shape of the incisional vulnus can readily be selected depending on such travel distance, to thereby form a desired incisional vulnus with an excellent auto-closable property.